Electron beam discharge device



c. LfHowE ETAL ELECTRN' BEAM DISCHARGE DEVICE May 26., 1959 Filed Jan. 24, 1957 FlG.l.

FIG.2.

. INVENTORS:

1 Y TE E w N Om (non P. T .L T E Mw A n MM E I O .H mC T W BYU) IUnited u States Patent() ELECTRON BEAM DISCHARGE DEVICE Conrad L. Howe, Tell City, and William E. Polster, Evanston, Ind., assignors to General Electric Company, a corporation of New York Application January 24, 1957, Serial No. 636,147

Claims. (Cl. 313-69) This invention relates to electron discharge devices of the electron beam type, wherein electron flow from a cathode to an anode follows one or more beam-like paths of predetermined size and shape.

One form of electron beam electron discharge device to which the present invention is particularly applicable is commonly referred to as a beam power pentode. In such a device the space electrons emitted by the cathode are drawn through a control electrode of foraminate construction, such as a wire grille or mesh, by the attraction of a foraminate accelerator or screen electrode having a positive bias with respect to the cathode, and electrons thence pass to the anode through the openings in the screen electrode and through a beam-forming aperture deiined by an additional beam-forming electrode. Such discharge devices have certain operating advantages, such as a sharp knee in the anode current vs. anode voltage characteristic, affording reduced signal distortion. For optimum efiiciency of such discharge devices, it is desirable that the electron beam be well defined and of uniform density, and that the electron ow between the cathode and the accelerator or screen electrode be minimized.

A principal object of the present invention is to provide an electron discharge device of the electron beam type which retains all the advantageous operating characteristics of prior art beam-type electron discharge devices yet has a substantially simplified structural form affording significant savings in manufacturing cost.

This and other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawing, and the scope of the invention will be defined in the appended claims.

Briefly, in accordance with the present invention, the need for a separate and distinct beam forming electrode in an electron discharge device of the electron beam type is eliminated, while retaining all the operating advantages associated with beam-type discharge devices, by covering selected portions of the accelerator screen electrode with electrically non-conducting material so as to define therebetween a beam-forming aperture, and a screen electrode so treated draws a reduced amount of current and thereby contributes to maximum operating efiiciency.

In the drawing:

Figure 1 is a partially broken away view of an electron discharge device constructed in accordance with the present invention;

Figure 2 is an enlarged cutaway perspective view of a portion of the structure shown in Figure 1,

Figure 3 is an enlarged transverse sectional view of the electron discharge device of Figs. l and 2.

Referring to the drawing, there is shown one illustrative embodiment of a discharge device constructed in accordance with the present invention, including an envelope 2 within which s enclosed a centrally located indirectly heated cathode 3 having emissive surfaces 4, 5.

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Surrounding the cathode 3 in spaced relation `therewith is a foraminate control grid 6 consisting of a somewhat attened helix of spaced turns of line wire wound on a pair of support rods 8, 10, and surrounding the control grid in spaced relation therewith is an accelerating or screen grid 12 consisting of another flattened helix of fine wire 14 wound on a pair of support rods 16, 18. The control grid 6 and screen grid 12 are mounted in coaxial relation with the 'cathode 3, and the corresponding support rods 8, 16 and 10, 18 are in alignment in a plane generally parallel to the emissive surfaces 4, 5. As is conventional, the individual wires of the screen grid are arranged so as to be hidden from the cathode by corresponding wires of the control grid. A coaxial cylindrical sheet metal anode or plate 20 in turn surrounds the screen grid 12 in spaced relation therewith. The several electrodes are supported between insulating spacers 22 which may be of mica, and which are secured to the support rods near their upper and lower ends.

In the operation of such discharge devices space electrons originating at the electron emissive surface of the cathode are attracted by the accelerator or screen grid and pass through the openings between the conductors of the control grid and screen grid to the anode. For proper performance it is desired that the electrons owing from the cathode 3 to the anode 20 be formed or focused into one or more well-defined beams of uniform density, in the present instance two in number and extending in opposite directions substantially normal to the plane of the support rods 16, 18. To this end there has heretofore been provided in such beam-type discharge devices one or more separate and additional electrodes between the screen grid and anode for the purpose of defining one or more apertures of suitable size and position such as to constrict the electron ow to the anode into the desired beam or beams. In a discharge device of the type herein above described, such beam forming electrodes may take the form of spaced sheet metal plates, for example, positioned near the screen grid support rods and arranged generally normal to the plane of the support rods, as shown for example in U.S. Patent 2,107,520.

In accordance with the present invention,- however, it has been discovered that the separate beam-forming electrodes customary in prior art devices can be eliminated, and one or more electron beams can be formed with the desired size, shape, homogeneity and electron density, by covering selected portions of the screen grid with a coating of electrically non-conductive material. Such coating material is shown at 24 in Figs. 2 and 3, and is applied to the screen grid so as to form one or more electronopaque shields or walls, which may be continuous or may consist of discretely coated individual turns of wire 14, depending on the thickness of the coating and the spacing of the turns of wire 14. The coated portions of the grid 12 are selected so as to define therebetween beam-forming windows or apertures 26, 28 of the desired shape and size. The beam-forming windows are traversed by uncoated conductors 14 of the screen grid between which and the cathode the necessary electrostatic field is set up to induce electrons to flow from thecathode to the anode, and the insulating coating material 24 serves to confine the electrostatic field flux to vthe areas of the windows, so that the electron ow is 'effectively concentrated into beams through the Windows, as illustrated diagramatically in Fig. 3. In the embodiment shown the coated portions are positioned so as to be bisected by the plane of the screen grid support rods 18, and thus deline electron beam paths generally normal to the plane of the support rods and to the cathode emissive surfaces 4, 5.

In addition to eliminating the need for separate beamforming electrodes, it is an additional advantage of the present invention that the portions of the screen grid coated with insulating material effectively block return of electrons from the anode into the beam path between cathode and screen, yet cannot absorb electrons, whether primary electrons from the vicinity of the cathode or secondary electrons backscattered from the anode, and thus the coated portions serve effectively as suppressor electrodes while minimizing screen grid current, with a corresponding increase in efficiency.

The coating material 24 may consist of any suitable non-conductive material which will not render the discharge device gassy and which is capable of withstanding the requisite environmental conditions of temperature, electron bombardment, etc. One suitable coating material, for example, is that conventionally employed as an insulative coating for larnentary heaters, consisting of a mixture of aluminum oxide and a suitable binder. The coating may be applied in any desired manner such as by spraying, dipping, cataphoresis, or the like.

From the foregoing description it will be apparent that the present invention provides an electron beam type of electron discharge device in which all the operating advantages of conventional beam-type discharge devices are retained yet which, by elimination of separate beamforming electrodes, is substantially simplified from a structural standpoint with attendant reduction in manufacturing cost. Moreover, in accordance with the invention screen grid current is effectively minimized, for optimum efiiciency.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may take various forms and embodiments other than those illustrative embodiments heretofore described. It is to be understood therefore, that the scope of the invention is not limited by the details of the foregoing description, but will be defined in the following claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. In an electron discharge device of the electron beam type, a cathode for emitting electrons, an anode, a control electrode between the cathode and anode formed to provide spaces through which electrons can flow, a screen electrode between the control electrode and anode formed to provide spaces through which electrons can flow, and means for forming the electron flow from the cathode to the anode into at least one beam, said beam forming means comprising a covering of electrically nonconductive material on selected portions of said screen electrode, said covering inhibiting ow of electrons to and through the portions of the screen electrode covered thereby and defining between said selected portions at least one electron transparent region of said screen electrode traversed by uncovered conductive portions of said screen electrode through which electrons can ow between the cathode and anode.

2. In an electron discharge device of the electron beam type, a cathode, an anode adapted to be maintained at a positive potential with respect to the cathode, an accelerator electrode between the cathode and anode adapted to be maintained at a potential positive with respect to the cathode for promoting electron ow between the cathode and anode, said accelerator electrode including electrically conductive portions formed to provide spaces through which electrons owing from the direction of said cathode may pass toward said anode, and means for forming the flow of electrons between the cathode and anode into a beam comprising a coating of electrically non-conducting material deposited directly on selected portions of said accelerator electrode.

3. In an electron discharge device of the electron beam type, a cathode having an electron emitting surface, an anode adapted to be maintained at a potential positive with respect to the cathode, a screen electrode between the cathode and anode consisting of a grille of spaced electrical conductors adapted to be maintained at a positive potential with respect to the cathode, a control electrode between the screen electrode and anode consisting of a grille of spaced electrical conductors adapted to be maintained at a potential negative with respect to the screen electrode, and means for forming the electron flow to said anode into at least one beam comprising electrically nonconductive material covering selected portions of the conductors of said screen electrode, said covering material inhibiting electron flow to and through the portions of the screen electrode covered thereby and said covering portions defining therebetween an electron beam-forming aperture traversed by uncovered portions of the conductors of said screen electrode through which electrons may flow from the direction of said cathode toward said anode.

4. In an electron discharge device as defined in claim 3, said non-conducting covering material on each of said selected portions of said screen electrode extending between adjacent conductors of the screen electrode grille so as to form a continuous integral electron-opaque wall.

5. In an electron discharge device as defined in claim 3, said non-conducting covering material forming discrete coatings on individual conductors of said screen electrode grille.

References Cited in the file of this patent UNITED STATES PATENTS 2,107,520 Schade Feb. 8, 1938 2,611,098 Rockwood Sept. 16, 1952 2,722,623 Law Nov. 1, 1955 2,728,021 Blanks Dec. 20, 1955 

